During a phone call, the Prime Minister and President called for action to ensure investigators are granted "unhindered access" to the crash site to bring those responsible to account.

"They both agreed that an independent investigation must get underway as soon as possible and that all countries should engage to ensure that pro- Russian separatists grant investigators secure and unhindered access to the crash site," a Downing Street spokesman said.

“They also discussed the further steps taken by the US and EU this week to make clear to Russia that there will be costs if they do not substantively engage in a peaceful resolution to the crisis and they agreed that to keep up the pressure in the weeks ahead if there is no progress towards de-escalation."